In recent years there has been widespread interest in the implementation of online courses in universities. While most studies about online learning environments primarily focus on technology-related issues or instructional methods, little attention has been given to online teachers and their teaching approaches. The aim of this paper is to provide an overview of how teachers approach online teaching and the factors affecting individual teachers approaches to teaching online, particularly in a fully online university. Nine hundred and sixty-five (965) online teachers belonging to the Open University of Catalonia were surveyed. The dependent variables include three approaches to teaching online: the Content Acquisition approach, the Collaborative Learning approach, and the Knowledge Building approach. The explanatory variables are socio-demographics, academic background, online teaching experience, studies taught, online teaching dedication, and teachers' roles in teaching online. Multiple regression analyses are used to make inferential judgements and test the effects of the independent variables. Findings suggest that age, academic background, online teaching dedication and, especially, teachers' roles in teaching online are important predictors of the adoption of a particular approach to teaching online.